With the continuous development of photography technology and image stitching technology, an ultra high definition image has gradually been widely applied for recording reliable data like astronomical observation, geological survey, aerial reconnaissance, security monitoring, antiques. This image has extremely high commercial value, and thus it is of vital importance to protect copyright of this image.
A digital watermark appears as an information hiding technology against the difficulty in judicially identifying copyright of digital products. In this technology, specific information is embedded into original data to be protected for verifying proprietorship of electronic data. As one of the important manners for announcing and protecting a general image copyright, the effects of this technology have been recognized to a certain extent. However, the ultra high definition image mentioned above goes beyond the ability of existing digital watermark algorithms. The reason for this mainly lies in that the ultra high definition image is rich in content and has a high resolution. A small portion of the image or a version of the image which is formed by reducing the image by a factor of a dozen still has a high collection value. The corresponding digital watermark solution is confronted with a large scale cropping attack and a large scale reducing attack, and these two kinds of attacks are blind spots for the conventional watermark algorithms.